On 05/25/2016 10:53 AM, Bart Van Assche wrote:
> On 05/25/2016 12:54 AM, mchristi@xxxxxxxxxx wrote:
>> If the __blk_mq_run_hw_queue is a result of a async run or retry
>> then we do not have a reference to the queue. At this time,
>> blk_cleanup_queue could begin tearing it down while the queue_rq
>> function is being run.
>>
>> This patch just has us do a blk_queue_enter call.
>>
>> Signed-off-by: Mike Christie <mchristi@xxxxxxxxxx>
>> ---
>> block/blk-mq.c | 10 +++++++++-
>> 1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 7df9c92..5958a02 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -738,8 +738,13 @@ static void __blk_mq_run_hw_queue(struct
>> blk_mq_hw_ctx *hctx)
>>
>> WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask));
>>
>> - if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
>> + if (blk_queue_enter(q, false)) {
>> + blk_mq_run_hw_queue(hctx, true);
>> return;
>> + }
>> +
>> + if (unlikely(test_bit(BLK_MQ_S_STOPPED, &hctx->state)))
>> + goto exit_queue;
>>
>> hctx->run++;
>>
>> @@ -832,6 +837,9 @@ static void __blk_mq_run_hw_queue(struct
>> blk_mq_hw_ctx *hctx)
>> **/
>> blk_mq_run_hw_queue(hctx, true);
>> }
>> +
>> +exit_queue:
>> + blk_queue_exit(q);
>> }
>
> Hello Mike,
>
> blk_cleanup_queue() waits until delay_work and run_work have finished
> inside blk_sync_queue(). The code in blk_cleanup_queue() before the
> blk_sync_queue() call should be safe to execute concurrently with
> queue_rq(). Or did I perhaps miss something?
>
My concern was when blk_mq_run_hw_queue is run with async=false then we
are not always run from the work queue or a under another
blk_queue_enter call already.
For example, in the scsi cases where we call
scsi_run_queue->blk_mq_start_stopped_hw_queues we can be in soft irq
context, some driver thread or the scsi eh thread.
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